Pension Plans and Other Postretirement Benefits - Changes in Level 3 Pension Plan Assets Measured at Fair Value on Recurring Basis (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2023 USD ($)
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Fair value of plan assets at beginning of year	$ 2,938
Fair value of plan assets at end of year	3,141
Significant Unobservable Inputs (Level 3) [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Fair value of plan assets at beginning of year	408
Fair value of plan assets at end of year	444
Real Estate Partnerships [Member] | Significant Unobservable Inputs (Level 3) [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Fair value of plan assets at beginning of year	20
Purchase(Sales)	2
Fair value of plan assets at end of year	22
Private Equity/Debt [Member] | Significant Unobservable Inputs (Level 3) [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Fair value of plan assets at beginning of year	211
Purchase(Sales)	12
Realized/Unrealized Gains (Losses)	12
Fair value of plan assets at end of year	235
Hedge Funds [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Fair value of plan assets at beginning of year	276
Fair value of plan assets at end of year	285
Hedge Funds [Member] | Significant Unobservable Inputs (Level 3) [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Fair value of plan assets at beginning of year	167
Realized/Unrealized Gains (Losses)	11
Fair value of plan assets at end of year	178
Guaranteed Deposit Fund [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Fair value of plan assets at beginning of year	10
Fair value of plan assets at end of year	9
Guaranteed Deposit Fund [Member] | Significant Unobservable Inputs (Level 3) [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Fair value of plan assets at beginning of year	10
Realized/Unrealized Gains (Losses)	(1)
Fair value of plan assets at end of year	9
Securities [Member] | Significant Unobservable Inputs (Level 3) [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Fair value of plan assets at beginning of year	408
Purchase(Sales)	14
Realized/Unrealized Gains (Losses)	22
Fair value of plan assets at end of year	$ 444